The majority of vacuum cleaners are either of the ‘upright’ type or of the ‘cylinder’ type, called canister or barrel cleaners in some countries. An upright vacuum cleaner normally comprises a main body containing dirt and dust separating apparatus, a cleaner head rotatably mounted on the main body and having a dirty air inlet, and a motor and fan unit for drawing dirty air into the dirt and dust separating apparatus via the dirty air inlet so that dirt and dust can be separated from the airflow before the clean air is expelled to the atmosphere. The dirty-air inlet through which dirty air is sucked into the vacuum cleaner is directed downwardly so that it faces the floor to be cleaned. The dirt and dust separating apparatus can take the form of a filter bag or, as is known, can alternatively take the form of a cyclonic arrangement. The present invention is not concerned with the nature of the dirt and dust separating apparatus and is therefore applicable to vacuum cleaners utilising either arrangement.
An agitator in the form of, for example, a brush bar is supported in the dirty-air inlet so that it protrudes to a small extent from the inlet. The brush bar typically comprises an elongate cylindrical core from which bristles extend along its length in a radial direction. The brush bar may be driven by a dedicated motor, typically via a drive belt, so that the brush bar rotates within the inlet. Rotation of the brush bar causes the bristles to flick dirt and debris from the fibres of the carpet to be cleaned. The suction of air causes air to flow around the brush bar and underneath it to help lift the dirt and dust from the surface to be cleaned and then carry it from the dirty-air inlet to the dirt and dust separating apparatus. Use of the agitator when cleaning a carpeted surface provides a superior cleaning performance than if an agitator is not used.
A problem which may be encountered with surface-treating appliances employing an agitator is that the agitator motor must be protected from overheating and/or overloading under adverse operating conditions which may arise. Such a situation may occur, for example, in the event the rotary agitator becomes jammed through engagement with the fringe of a rug or other object that prevents or restricts rotation of the agitator.